Signs a cat needs a playmate?

I'm hoping someone could tell me what i should look for to see if my cat trouble needs a playmate. I adopted trouble and dingle together as kittens 3 years ago, they were part of the same litter. Dingle passed away unexpectedly last Friday, leaving trouble semi alone. I have another cat Missy who is FIV+ and stays in her own special bedroom in the house. they play under the door, but i dont let other contact for fear of spreading the virus. Since Saturday, trouble went from being a cat that liked to play with us sometimes, to every second we are around wanting to play. I'm wondering if its because he used to play with dingle during the day when we were at work, so now hes bored? Im sure its a huge adjustment for him to not have his playmate around for the first time in his life.

Also how long should i wait before getting another cat if thats the case? i dont want him to "forget" other cats exist.

Thanks,

Mandy

i was reading about a couple posters said that. I tried it a little tonight and trouble still hisses at her face to face but plays under the door. She likes trouble and gets the most confused look on her face and then when she goes back to her room she talks to him under the door. I'm not sure what Troubles deal is, unless its cuz shes a long haired cat and hes not? shes been inside with us over a year now. If she didnt have FIV i would just let them sort it out, but im afraid if it gets too serious then trouble will catch the virus from her.